This invention relates to polyester alloy compositions having unexpectedly high impact strengths. More particularly, the invention relates to moldable polyester alloys comprising blends of amorphous polyesters with graft polymers which exhibit unexpected improvement in impact properties. The amorphous polyesters are the copolyesters of aromatic dicarboxylic acids and of aliphatic diols and include copoly(1,4-cyclohexylene dimethylene iso/terephthalate) (PCDT) and the like, and the graft polymers are polymers of a vinyl aromatic hydrocarbon, an alkylacrylate and, optionally, an acrylonitrile prepared in the presence of a rubbery diene substrate.
Aromatic polyesters of aliphatic diols are widely used as molding plastics, however they generally exhibit low impact properties, and high notch sensitivity limits their use. Prior art efforts to overcome these limitations have met with only moderate success. For example, in U.S. Pat. No. 3,644,574, blends of poly(tetramethylene terephthalate) (PTMT) with polystyrene or copolymers having greater than 50% styrene content are disclosed which exhibit modest improvement in impact properties. This technique succeeded only with PTMT, and no improvement of impact properties was obtained for blends with poly(ethylene terephthalate) or poly(trimethylene terephthalate). In U.S. Pat. No. 3,564,077, moderate impact improvement was effected in poly(ethylene terephthalate) when small amounts, generally less than 10% by weight, of styrene-butadiene copolymers were blended therewith. In general, these and other prior art methods have not produced moldable polyesters having the extremely high impact necessary for use as engineering thermoplastic materials.